1 Field of the Invention
The present invention relates to a steering lock device in which a rotor is made rotatable by insertion of a key and inserted into a fixed cylinder, a housing having a guide projection inserting into an insertion hole of a steering column pipe is mounted to the steering column pipe, and a lock mechanism having a lock pin in a square cross-sectional shape engageable with an engagement recess of a steering shaft is constituted to enable engagement and disengagement of the lock pin with and from the engagement recess to be switched in accordance with the rotation of the rotor.
2 Description of the Prior Art
The above steering lock device has already been known, for example, by Japanese Utility Model Publication Nos. 15080/1988 and 27891/1991.
A lock pin of a lock mechanism undergoes a bending load by a rotational torque of a steering shaft in a state in which the lock pin is engaged in an engagement recess. In the lock pin of the steering lock mechanism, the modulus of section Z is represented as: (Z=(1/6).multidot.H.multidot.B.sup.2) where H is a length of a first side along the axial line of the steering shaft and B is a length of a second side orthogonal to the first side. In order to increase the flexural strength of the lock pin by making the modulus of section larger, the length B was set relatively largely, for example, the lengths B, H were set as: 1.gtoreq.B/H.gtoreq.0.5.
However, if the flexural strength of the lock pin is excessively large, the strength of the contact portion between a guide projection and an insertion hole provided in the steering column pipe into which the guide projection is inserted becomes relatively lower than the above mentioned flexural strength and, as a result of which, the insertion contact portion of the guide projection and the insertion hole is deformed before the lock pin is deformed. Therefore, the flexural strength of the lock pin and the strength of the insertion contact portion between the guide projection and the insertion hole have to be balanced with each other for improving the strength limit of the lock mechanism.
Further, in a structure in which the guide projection provided in the housing is inserted into the insertion hole provided in the steering column pipe, and the lock pin protruded from the guide projection is engaged with the engagement recess in the steering shaft, bending load is exerted from the lock pin to the guide projection of the housing in the engagement state of the lock pin into the engagement recess, and a reaction is exerted on the guide projection from the contact portion of the insertion hole and the guide projection. According to the result of the studies of the present inventor, it has been proved that the strength of the guide projection is lowered depending on the offset amount between the operation point of the bending load and the operation point of the reaction. Then, it is necessary to appropriately determine the offset amount on every steering lock device in order to maintain the strength of the guide projection. In this case, if an appropriate offset amount can be determined in accordance with the dimensions of the parts constituting the steering lock devices, it can contribute to the rationalization of the productivity.
In addition, if the lock mechanism having a relatively great number of parts can be simplified and the number of parts can be reduced, the assembling operation for the lock mechanism can also be facilitated.